Flare systems are used in petroleum refineries and chemical processing plants for burning flammable, explosive, and/or hazardous materials which are vented from processing systems and equipment as a result of overpressure or other upset conditions. Vertical flare stacks used in refineries and chemical plants can be as much as 500 feet or more in height. The materials vented to the flare system are discharged from the upper end of the flare stack where they are immediately ignited by one or more continuously burning flare pilots.
In order to ensure that the dangerous gases discharged from the top of the flare stack are ignited and burned, flare pilot monitors are commonly used for automatically sensing the presence of the pilot flame and notifying the operator in the event that the pilot flame has gone out. The monitoring system will also typically be linked to a controller and relighting device which will automatically relight the flare pilot flame in the event that an outage occurs.
Flare pilot monitoring systems typically employ thermocouple temperature sensors positioned within the pilot burner at the top of the flare stack. Unfortunately, due to the extreme temperature conditions and temperature swings experienced during operation at the top of the flare stack, the thermocouples tend to have a relatively short service life and must be frequently replaced.
To avoid the necessity of shutting down the flare system, and potentially the entire refinery or chemical plant, when removing and replacing a flare pilot sensor, retractable thermocouples are used which can be installed at grade. Consequently, these retractable thermocouples can be installed or replaced while the flare stack remains in operation.
The retractable thermocouple will typically be unwound from a spool and pushed through a stainless steel conduit extending up the vertical flare stack. The retractable thermocouple must be pushed through the thermocouple tubing until a sensing tip on the end of the thermocouple is seated within a thermowell inside the flare pilot burner. The thermocouple tubing is preferably routed up the flare stack with long radius bends which assist in allowing the retractable thermocouple to be pushed as freely as possible through the lengthy vertical tubing to the top of the flare stack.
Unfortunately, however, the frictional and gravitational forces experienced while pushing the retractable thermocouple up the lengthy vertical tubing can make the delivery of the retractable thermocouple to the top of the flare stack extremely difficult and can oftentimes prevent the sensor tip from being fully delivered into the flare pilot thermowell. Moreover, the frictional forces encountered when attempting to push the retractable thermocouple to the top of the flare stack through the thermocouple tubing can be severely exacerbated due to kinks, bends, or other irregularities which are inherently produced when coiling and uncoiling the retractable thermocouple, or are otherwise formed in the thermocouple during production, shipping, storage, and use.
The devices developed heretofore for attempting to remove kinks, bends, and other irregularities from retractable thermocouples have had significant shortcomings and disadvantages. These prior art devices have typically consisted of an offset cyclic straightener which will displace the thermocouple slightly from its center axis so as to slightly cold-work the thermocouple sheath. The offset spins around the thermocouple axis so as to cold-work the thermocouple in a direction which will hopefully erase any previous “memory” of the sheath and thus straighten the thermocouple.
The use of these prior straightening devices has been inadequate and problematic because the devices are susceptible to damaging and breaking the thermocouple and the devices add frictional resistance to the thermocouple insertion process. The devices also require that the thermocouple be moved continuously through the straightener. Otherwise, the cyclic bending will fatigue the thermocouple sheath and damage or break it, thus rendering the thermocouple inoperable. Also, if the pushing force applied is inconsistent or insufficient, the operation of the device must be interrupted. Further, the prior devices require that the thermocouple pass through and contact several ferrules which add significant amounts of sliding friction to the already problematic resistance which must be overcome during installation.
In addition to straightening, a need exists for an improved apparatus for pushing the retractable thermocouple through the thermocouple tubing to the top of the flare stack. Heretofore, retractable thermocouples have either been manually pushed to the top of the flare stack by hand or have been pushed through the thermocouple tubing using driven metal wheels. The metal wheels have a tendency to slip due to low contact friction and, in doing so, the metal wheels may damage the thermocouple sheath.
The use of the prior thermocouple pushing device has also been inadequate and problematic because the attempted straightening and pushing functions have been conducted by separate devices. The prior art straightening method requires significant pushing force for just the straightening process alone. However, even without the additional resistance imported by the straightener, the pusher is often still incapable of pushing the thermocouple to its complete length.